Bump version number to 0.14.3

Summary: As per title. We just released 0.14.2 , so that's the next step.

Test Plan:

make check

Reviewers: freetrader, sickpig, awemany, kyuupichan, #bitcoin_abc

Reviewed By: freetrader, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D319